In the image reading apparatus such as an image scanner, copying machine and so on, a contact image sensor unit which is brought into close contact with the original to read the original at the same magnification has been conventionally used as the image sensor optically reading image information on the original and converting the information into electric signals.
The contact image sensor unit is used while being attached below a transparent original supporting body supporting the original in the image reading apparatus. There are two main methods of attaching the contact image sensor unit in the image reading apparatus as follows.
(1) A flatbed-type in which reading is performed by moving the image sensor unit with the original fixed on the original supporting body of the image reading apparatus.
(2) A sheetfeed-type in which reading is performed by moving the original on the original supporting body with the image sensor unit fixed to the image reading apparatus.
These examples are disclosed in Patent Literature 1.
It is known that in a configuration example of the conventional contact image sensor unit used for them, an illumination device composed of a light source using an LED for illuminating the original and a light guide is attached to a frame. This illumination device is composed of a light guide which takes in emitted light from the light source and emits the light so that the illumination amount becomes almost uniform over the length of one line of an original reading part. Further, the frame also includes a sensor substrate on which a sensor array formed by arranging a plurality of photoelectric conversion elements including a plurality of light receiving parts performing photoelectric conversion of an optical image of the original into electric signals in lines is mounted, and a lens array forming an optical image of the original on the sensor array. Further, a connector electrically connecting the sensor array to an external device is attached to the sensor substrate.
The conventional contact image sensor unit is attached below a transparent glass being the original supporting body in the above-described type (1). On the other hand, a transparent glass being the original supporting body is attached on the contact image sensor unit in the above-described type (2).
Here, when the light guide is fixed to the frame of the contact image sensor unit with an adhesive or the like, there are following problems. Specifically, the materials of the frame and the light guide are different, thus possibly causing poor conditions such as the deformation of the light guide caused by the thermal expansion and/or contraction due to a change in environmental temperature, and the warpage of the contact image sensor unit and the like.
In Patent Literature 2, to cope with the thermal expansion difference and thermal contraction difference generated between the frame and the light guide constituting the illumination device, an image sensor as illustrated in FIG. 14 is proposed. An image sensor (a contact image sensor unit) 400 illustrated in FIG. 14 irradiates an original with light from a line illumination device to image reflection light from the irradiated original on a light receiving element array (photoelectric conversion element) 402 by a lens array (imaging element) 401 and then reads the image. Further, the line illumination device (illumination device) is composed of a light emitting element (light source) and a light guide 403. The light guide 403 is structured to be pressed against a frame 406 by a claw part 405 provided at the tip of an elastic holding part 404. Therefore, even when there is a thermal expansion difference or thermal contraction difference between the line illumination device and the frame 406, there is no stress occurring between them, resulting in no poor condition such as warpage or the like on the image sensor 400. Further, it is also disclosed that since the line illumination device is fixed to the frame 406 of the image sensor 400 by the elastic holding part 404, the line illumination device can be easily detached.
However, in this conventional technique, it is difficult to integrally mold the frame 406 and the elastic holding part 404 which needs to be made of a material having elastic characteristics different from that of the frame 406 and have a complicated shape in consideration of the shape and the detachability of the light guide 403 and the like.
Furthermore, there is a problem in terms of production management of the contact image sensor unit production as follows.
There is a demand to make the outside dimensions of frames uniform in order to commonalize the assembly work and related peripheral components. However, there are variations in the specifications, shape, attachment position, direction of emitted light and so on of the light guide used in the contact image sensor unit. For example, is necessary to prepare light guides in various shapes to cope with the illumination angle or direction due to the difference in distance between the contact image sensor and the original, and to cope with various modifications in the attachment position and angle of the light guide to the frame.
Accordingly, in the production of the contact image sensor unit, it is necessary to prepare many kinds of individual frames to cope with the difference in shape, attachment position and angle of the light guide, requiring labor in production management. Further, FIG. 12 of the above-described Patent Literature 2 discloses a CIS unit in which two line illumination devices are arranged to be substantially symmetric about a lens array located at the middle. The two structures of the light guides and the cases housing the light guides used in the line illumination devices are the same. Further, in Patent Literature 1, the two right and left light guides are configured to be different in irradiation angle and position to the lens array at the middle in order to increase the illumination depth, thereby increasing the quality of the image sensor unit in terms of the illumination depth and the illumination amount to the original.